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C. R. Palevol 13 (2014) 205–221

Contents lists available at ScienceDirect

Comptes Rendus Palevol

w w w.sc i encedi rec t .com

uman palaeontology and prehistory (Palaeoanthropology)

rigonid crests expression in Atapuerca-Sima de los Huesosower molars: Internal and external morphologicalxpression and evolutionary inferences

xpression des crêtes du trigonide de molaires inférieures àtapuerca-Sima de los Huesos : expression morphologique interne etxterne et inférences évolutionnistes

arina Martínez de Pinillosa,∗, María Martinón-Torresa,atthew M. Skinnerb,c, Juan Luis Arsuagad, Ana Gracia-Téllezd,e,

gnacio Martínezd,e, Laura Martín-Francésa, José María Bermúdez de Castroa

Hominid Dental Research Group, National Research Center on Human Evolution (CENIEH), Paseo Sierra de Atapuerca s/n, 09002urgos, SpainDepartment of Anthropology, University College London, 14, Taviton Street, London, WC1H 0BW, United KingdomDepartment of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103, Leipzig, GermanyCentro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos, Avd. Monforte de Lemos 5, Pabellón 14, 28029 Madrid, SpainÁrea de Paleontología, Departamento de Geología, Universidad de Alcalá de Henares, 28871 Alcalá de Henares, Spain

a r t i c l e i n f o

rticle history:eceived 23 May 2013ccepted after revision 18 October 2013vailable online 10 February 2014

andled by Yves Coppens

eywords:ermanent lower molarsomo heidelbergensisima de los Huesosomo neanderthalensisomo sapiens

a b s t r a c t

Trigonid crest patterning in lower molars is distinctive among Late Pleistocene homininssuch as Homo neanderthalensis, fossil Homo sapiens and modern humans. In this paper, wepresent an examination of trigonid crest patterning in the Middle Pleistocene permanentlower molar sample (n = 62) of Homo heidelbergensis from Sima de los Huesos (SH). Crestexpression was assessed from 3D models of the enamel and the dentine surfaces that wereproduced using micro-computed tomography (microCT). The aims of our analysis are to:1) characterize the pattern of trigonid crest expression at the outer enamel and enamel-dentine junction surfaces (OES and EDJ) of the SH sample, 2) evaluate the concordance ofexpression between both surfaces, and 3) place trigonid crest variation in the SH sampleinto a phylogenetic context. Our results reveal a greater variability in the expression oftrigonid crests at the EDJ (14 types) compared to the OES (4 types). Despite this variability,in almost all cases the expression of a continuous mid-trigonid or distal crest at the OES

icrotomographyrigonid crest patterns

corresponds with the expression of a continuous mesial/mid-trigonid or distal trigonidcrest, respectively, at the EDJ. Thus, it is possible to predict the type of trigonid crest patternthat would be at the OES in the case of partially worn teeth. Our study points to increasedvariability in trigonid crest expression in M3s compared to M1s and M2s. Moreover, ouranalysis reveals that the SH sample matches broadly the trigonid crest patterns displayedby H. neanderthalensis and differs from those exhibited by H. sapiens, particularly in thealmost constant expression of a continuous middle trigonid crest at the EDJ. However,SH hominins also exhibit patterns that have not been reported in H. neanderthalensis and

∗ Corresponding author.E-mail addresses: marinampg@hotmail.com, marina.martinezdepinillos@cenieh.es (M. Martínez de Pinillos).

631-0683/$ – see front matter © 2013 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.ttp://dx.doi.org/10.1016/j.crpv.2013.10.008

206 M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221

H. sapiens samples. Other aspects of the variability of the trigonid crest expression at thedentine are presented and discussed.

© 2013 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Mots clés :Molaires inférieures permanentesHomo heidelbergensisSima de los HuesosHomo neenderthalensisHomo sapiensMicrotomographieConfiguration des crêtes du trigonide

r é s u m é

La configuration de la crête du trigonide des molaires inférieures est caractéristique chezles homininés du Pléistocène supérieur, Homo neanderthalensis et Homo sapiens fossile, etaussi chez les humains actuels. Dans cet article, nous présentons l’examen de la configura-tion de la crête du trigonide d’un échantillon de molaires inférieures permanentes (n = 62)attribuées à Homo heidelbergensis, du site Pléistocène moyen de Sima de los Huesos (SH),en Espagne. L’expression de la crête est établie en modélisant les surfaces de l’émail et de ladentine à l’aide de rendus virtuels 3D basés sur un registre microtomographique (microCT).Le but de notre analyse est : 1) de caractériser le degré d’expression et la configurationde la crête du trigonide à la surface externe de l’émail (OES) et au niveau de la jonctionémail–dentine (EDJ) de l’échantillon SH, 2) d’évaluer la concordance d’expression entre lesdeux surfaces et 3) de replacer le degré de variation de la crête du trigonide observé au seinde l’échantillon SH dans un contexte phylogénétique. En comparaison de celle observée surl’OES (quatre types), nos résultats révèlent une grande variabilité dans l’expression de lacrête du trigonide au niveau de l’EDJ (14 types). Malgré cette variabilité, dans presque tousles cas, l’expression d’une crête du trigonide intermédiaire ou distale continue sur l’OES cor-respond respectivement à l’expression d’une crête du trigonide mésiale/intermédiaire oudistale continue au niveau de l’EDJ. Ainsi, à partir de l’analyse de la morphologie interne, ilest possible de prévoir le type de configuration de la crête du trigonide ayant existé sur l’OESdans le cas de dents partiellement usées. Notre étude souligne une variabilité croissantedans l’expression de ce trait sur les M3s par rapport aux M1s et M2s. En outre, notre étuderévèle que le degré de variation des configurations de la crête du trigonide dans l’échantillonde SH s’accorde avec celui observé chez H. neanderthalensis, mais qu’il diffère de celui deH. sapiens, en particulier dans l’expression presque constante d’une crête du trigonide inter-médiaire continue au niveau de l’EDJ. Cependant, les homininés de SH révèlent aussi desconfigurations qui n’ont pas été observées chez H. neanderthalensis et H. sapiens. D’autresaspects de la variabilité dans l’expression de la crête du trigonide au niveau de la dentinesont présentés et discutés.

émie d

© 2013 Acad

1. Introduction

Variation in dental form, as well as the frequency anddegree of expression of many dental traits are highly herita-ble, making teeth more useful than other skeletal elementsto assess phylogenetic relationships among fossil homininsand modern humans (Hrdlicka, 1923; Kaifu et al., 2005;Martinón-Torres et al., 2007, 2012). The expression of mor-phological traits has been traditionally recorded in theouter enamel surface (OES), but other researchers, particu-larly during the last decade, have attempted to characterizethe expression of these features at the enamel-dentinejunction (EDJ) (Bailey et al., 2011; Macchiarelli et al., 2006;Skinner et al., 2008a,b). It is assumed that the morphologyof the EDJ is largely responsible of the external morphol-ogy of a tooth (e.g., Guy et al., 2003; Nager, 1960; Schwartzet al., 1998). According to Korenhof (Korenhof, 1982; Scottand Turner, 1997) the EDJ morphology is more evolution-arily conservative than the OES morphology because “theenamel-dentine partition is much more a genetic blueprintof the occlusal anatomy of the teeth” (page 350 fromKorenhof, 1982). However, the precise level of concordancebetween both surfaces is still under study (e.g., Bailey et al.,

2011; Skinner et al., 2008b, 2009, 2010).

In the past, in order to analyze the EDJ surfaceit was necessary to employ destructive techniques toremove the enamel cap, or that the teeth were broken or

es sciences. Publié par Elsevier Masson SAS. Tous droits réservés.

incomplete (e.g., Corruccini, 1998; Korenhof, 1982; Nager,1960; Suzuki and Sakai, 1973). More recently, theincreasing availability of high-resolution micro-computedtomography (microCT) allows the virtual separation of thedifferent tissues that compose a tooth, a process that is alsocalled segmentation. From this segmentation, it is possibleto obtain accurate three-dimensional (3D) reconstructionsof detailed morphological features on both the OES and EDJin a non-destructive manner. In this sense, dental microCTstudies are expanding traditional analyses of discrete mor-phological traits to include their initial development onthe inner enamel epithelium prior to enamel deposition;a methodology which has been shown to greatly improveour understanding of their ontogeny and variability withinand among species (e.g., Ortiz et al., 2012; Skinner et al.,2008a,b).

The expression of trigonid crests on the enamel surfaceof human molars has revealed certain patterns of variationthat seem to be taxonomically and phylogenetically infor-mative (e.g., Bailey, 2002a; Irish, 1998; Scott and Turner,1997; Turner et al., 1991; Zubov, 1992a). From an evo-lutionary point of view, the primitive mammalian cusppattern in molars was a triangle (Vandebroek, 1967; Zubov,

1992b) (see Fig. 1.3 and Fig. 1.25 from Hillson, 2005). Inhumans, as in most primates, the mesial or anterior partof the lower molars is called the trigonid (trigon in uppermolars), and the distal or posterior part of the lower molars

M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221 207

Table 1Study sample of lower molars.Tableau 1Liste des molaires inférieures étudiées dans ce travail.

Species Origin N total M1 (n) M2 (n) M3 (n)

H. heidelbergensis Sima de los Huesosa 62 22 18 22

H. neanderthalensis Engisb 1 1 – –Gibraltarb 3 2 1 –Ehringsdorfc 1 1 – –Abri Bourgeois-Delaunayc 1 1 – –Regourdouc 6 2 2 2Abri Suardc 4 3 – 1Krapinac 20 7 6 7Hunasc 1 – – 1Roc de Marsalc 2 2 – –

H. sapiens Equus Caveb 2 2 – –Qafzehb 8 4 4 –Lagar Velhoc 1 1 – –El Miradora 9 3 3 3CENIEHa 12 4 7 1

i2cmeta

1b2tiflttTcdttiedth

tlsb(dpmhdt

a CENIEH micro-computed tomography data base.b ESRF© data base.c NESPOS© data base.

s the talonid (talon in upper molars) (White and Folkens,005). Trigonid crest refers to the expression of a crest thatonnect the first (protoconid) with the second (metaconid)ain cusps in lower molars (Scott and Turner, 1997; Turner

t al., 1991) and it can arise from any lobe segment or fromhe marginal ridge complex as well (Bailey et al., 2011; seelso below).

Following the pioneer work of Korenhof (Korenhof,982; Scott and Turner, 1997), trigonid crests have recentlyeen studied at the EDJ by means of microCT (Bailey et al.,011; Skinner et al., 2008b). These studies have confirmedhat the distinctive trigonid crest expression at the OESn Neanderthals is matched at the EDJ, both in terms ofrequency and morphology (Bailey et al., 2011). In particu-ar, the expression of conspicuous and continuous middlerigonid crests in lower molars has been interpreted asypical of Homo neanderthalensis (Bailey, 2002b; Martinón-orres, 2006). We now know that this species is not onlyharacterized by the high frequency of expression of mid-le trigonid crests, but also that the structures underlininghis crest in the dentine may be different to the oneshat contribute to the middle trigonid crest expressionn other hominin species (Bailey et al., 2011). However,volutionary origin and timing of this distinctive Nean-erthal pattern remain unclear, as the EDJ expression ofhe trait has not been examined in geochronologically olderominin species.

In this study, we aim to investigate the expression ofrigonid crests at EDJ of the Atapuerca-Sima de los Huesosower molar sample by means of microCT. Sima de los Hue-os site is a small cavity of approximately 8 m2 × 4 m2 thatelongs to the Cueva Mayor-Cueva del Silo karst systemAtapuerca, Spain). This site has provided the largest Mid-le Pleistocene Homo fossil record coming from the samelace and, to date, the human fossils recovered sum up

ore than 6500 remains, about the 80% of the worldwide

uman fossil record for the Middle Pleistocene (Bermúdeze Castro et al., 2004a,b). This extraordinary accumula-ion gives us the opportunity to study intrapopulation

variability in a fossil population (Arsuaga et al., 1991, 1993,1997; Bermúdez de Castro et al., 2004; Martinón-Torreset al., 2012). Sima de los Huesos hominins have beenassigned to Homo heidelbergensis, a species that has beeninterpreted as ancestral to H. neanderthalensis, althoughthe exact relationship between both taxa is still matterof debate (Arsuaga et al., 1997; Hublin, 2009; Martinón-Torres et al., 2012; Mounier et al., 2009). Our objectives areto:

• characterize the pattern of trigonid crest expression atthe OES and EDJ of the SH sample;

• evaluate the concordance of expression between bothsurfaces;

• place trigonid crest variation in the SH sample into aphylogenetic context and in particular in relation toH. neanderthalensis.

2. Materials

2.1. The Sima de los Huesos dental sample

Although the SH dental sample consists of 213 perma-nent molars, of which 123 are lower molars, we have onlyincluded in this study those that were isolated or includedin a mandibular fragment small enough to fit in the microCTscanner. In addition, and following Bailey et al. (2011), weexcluded those with wear degree higher than category 5(Molnar, 1971).

2.2. Comparative sample

We compare the SH molars to a sample ofH. neanderthalensis specimens and to a sample of early andcontemporary H. sapiens, since the latter is considered

the sister lineage of H. neanderthalensis (Table 1). TheNeanderthal and H. sapiens samples were taken fromNESPOS© and ESRF© data bases, from El Mirador Cave– an archaeological site located at the southern side of the

l. / C. R. Palevol 13 (2014) 205–221

Fig. 1. Scheme of some of the molar crown structures used in this study.MS: mesial segment; ES: essential segment; DS: distal segment; CT: cusptip.

208 M. Martínez de Pinillos et a

Sierra de Atapuerca with human remains from Calcoliticand Bronze Ages (Cáceres et al., 2007) – and from CENIEH’sdental collection, composed of clinically extracted teethfrom patients of known age and sex, representing amodern Spanish population.

3. Methods

Each molar of the SH sample and the contempo-rary H. sapiens sample, as well as those from El Mirador,was scanned with a Scanco Medical AG Micro-ComputedTomography 80, housed at the CENIEH. The Scanco Medi-cal Micro-CT80 system is characterized by a maximum scansize diameter of 75.8 mm and a maximum scan length of140 mm, with image matrix from 512 × 512 to 4096 × 4096pixels. Scans of the H. heidelbergensis teeth from Sima delos Huesos used a peak energy of 70 kV and intensity ofscanning of 114 �A. The sample time of one projectionis 800 000 �s, and the microCT takes nearly 500 paral-lel projections for each 180◦. The resultant slice thicknessranged from 18 to 36 micrometers (�m). Segmentation ofthe microCT volume was done semi-automatically withmanual corrections using AMIRA 5.3.3 (Visage Imaging,Inc.) and no filters were applied. For the rest of the compar-ative dental sample, we have obtained the microCT scansfrom the NESPOS© and ESRF© databases.

3.1. Terminological considerations and scoringprocedures

Dental literature has been employing different termi-nologies to refer to the same anatomical parts (e.g., Baileyet al., 2011; Carlsen, 1987; Korenhof, 1982; Martinón-Torres et al., 2012; Scott and Turner, 1997; Turner et al.,1991; Wu and Turner, 1993). In order to avoid confusionand to allow the reproducibility of our method amongresearchers, we specify below the terms and the termi-nology sources we have used in this manuscript (Fig. 1).These terms and terminology are based on morphology ofthe OES. We consider a cusp an occlusal projection from thecrown (White and Folkens, 2005) that is typically made upof three different segments (also called accessory lobes byScott and Turner, 1997): mesial, middle or essential, anddistal. The middle or essential segment is the lobe bear-ing the cusp (Carlsen, 1987; Scott and Turner, 1997), andthe free apex on top of the essential segment will be calledcusp tip (note that Carlsen, 1987, called it essential cusp,but Scott and Turner, 1997, simply call it cusp).

Arising from these concepts about the basic componentsof a molar, we can now discuss the different terminolo-gies published so far to refer to the trigonid crests. In 1982,Korenhof analyzed deciduous molars and defined a mesial(sic) trigonid crest – although Wu and Turner (1993) andBailey et al. (2011) assumed that Korenhof also called itmiddle trigonid crest – and a distal trigonid crest. Thesecrests were joining the mesial and the distal parts, respec-tively, of the two main mesial cusps of a lower molar. Wu

and Turner (1993) defined a middle and a distal trigonidcrest, but they did not find individuals expressing bothcrests at the same time. According to them, when a com-plete crest connects the middle portions of the mesial cusps

Fig. 1. Schéma de quelques structures de couronne de molaires utiliséesdans cette étude. MS : segment mésial ; ES : segment essentiel ; DS : seg-ment distal ; CT : pointe de la cuspide.

and it lies mesialward, but not on the marginal border,it should be called a middle trigonid crest; otherwise itwould be a distal trigonid crest. Scott and Turner (1997)only described a distal trigonid crest, defining it as a crest orridge that courses buccolingually along the distal aspect ofthe primitive trigonid, now represented by the protoconidand metaconid.

Finally, in recent studies, Skinner et al. (2008b) andBailey et al. (2011), scored crests at the EDJ based on theirorigin and the relative position of one to another, defin-ing a mesial, a middle and a distal trigonid crest. Accordingto them, a mesial trigonid crest could occur between themesial marginal ridge and the middle trigonid crest or evenbetween cusp tips as far as its position is substantiallymesialward within the tooth contour [although accordingto Carlsen’s terminology (Carlsen, 1987) that would be amiddle-middle crest]. Although we acknowledge the atyp-ical mesial position of some middle trigonid crests (Fig.9b from Bailey et al., 2011), in order to standardize termsto discuss anatomy in such a detail, we have preferred tosubscribe to the notion the middle or essential segmentis the one bearing the cusp tip (Carlsen, 1987; Scott andTurner, 1997). Within this framework, we propose that thethree types of crests should be scored independently of thepresence/absence of the other, in a similar way as they arescored at the OES (e.g., Guatelli-Steinberg and Irish, 2005;Martinón-Torres et al., 2012).

Methodologically, to score the trigonid crests we draw astraight line from the protoconid to the metaconid tip. Any

trigonid crest lying distal to this line is classified as a dis-tal trigonid crest (DTC), and over or mesial to this line asa middle (MdTC) or mesial trigonid crest (MeTC) (Fig. 2).If one of the ends of the crest that runs along the mesial

M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221 209

Fig. 2. (Color online.) A. Occlusal enamel surface of AT-2271 (M3) from Sima de los Huesos (SH) illustrating a middle trigonid crest (MdTC) and a distaltrigonid crest (DTC). B. Occlusal dentine surface from AT-2271 illustrating a corresponding middle trigonid crest (MdTC) and a distal trigonid crest (DTC).C. Dentine from AT-143 (M3) of the SH site where we can see a mesial trigonid crest (MeTC). The green line from protoconid tip to metaconid tip definesthe position and classification of the crests.Fig. 2. (Couleur en ligne.) A. Surface occlusale d’émail d’AT-2271 (M3) de SH illustrant une crête du trigonide intermédiaire (MdTC) et une crête du trigonidedistale (DTC). B. Surface occlusale de dentine d’AT-143 (M3) du site SH où l’on observe une crête du trigonide médiale (MeTC). C. La ligne verte depuis lapointe du protoconide jusqu’à la pointe du métaconide définit la position et la classification des crêtes.

Fig. 3. (Color online.) Top: scheme of the four basic types of trigonid crests on enamel surface identified in our study. Scheme represents the occlusalsurface at the outer enamel surface (OES) including the tips of the cusps (represented by the open circles) of the protoconid and metaconid (mmr: mesialmarginal ridge). Explanation in the text. Bottom: examples of different types of trigonid crests on the enamel surface: type A (AT-946); type B (AT-2385);type C (AT-2271); type D (AT-943).Fig. 3. (Couleur en ligne.) En haut : schéma des quatre types de base des crêtes du trigonide sur la surface de l’émail identifié dans notre étude. Le schémareprésente la surface occlusale au niveau de l’OES incluant les pointes des cuspides (représentées par les cercles ouverts) des protoconide et métaconide(mmr : arête marginale mésiale). Explication dans le texte. En bas : exemples de différents types de crêtes du trigonide sur la surface de l’émail : type A(AT-946) ; type B (AT-2835) ; type C (AT-2271) ; type D (AT-943).

Based on Korenhof, 1982.

210 M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221

Table 2Percentages and frequencies of the continuous middle (MdTC) and distal trigonid crest (DTC) at the OES (only one antimere included). We consider thetrait is “present” when the crest is continuous. Otherwise we consider that the trait is “absent”.Tableau 2Pourcentages et fréquences des crêtes du trigonide intermédiaires (MdTC) et distales (DTC) au niveau de l’OES (un seul antimère inclus). Le trait est considérécomme « présent » lorsque la crête est continue. Sinon, le caractère est considéré comme « absent ».

Total molar sample M1 M2 M3

Middle trigonid crest at OESSH 93.0% (40/43) 100.0% (14/14) 100.0% (11/11) 83.3% (15/18)H. neanderthalensis 97.0% (33/34) 100.0% (16/16) 100.0% (8/8) 90.0% (9/10)H. sapiens 39.2% (11/28) 50.0% (6/12) 25.0% (3/12) 50.0% (2/4)

Distal trigonid crest at OESSH 25.5% (11/43) 0.0% 0.0% 61.1% (11/18)

6.2% (0.0%

omo ne

H. neanderthalensis 20.5% (7/34)

H. sapiens 0.0%

OES: outer enamel surface; SH: Sima de los Huesos; H. neanderthalensis: H

aspect of the protoconid and metaconid goes to the mesialmarginal ridge we define it as a MeTC. If not, we define it as aMdTC [what Korenhof (1982) calls mesial trigonid crest, inour study is considered as a middle trigonid crest]. We areaware that this method may imply some problems in thecase of teeth with more atypical shapes and where the cusptips are displaced. However, it relies in the anatomical com-ponents of a tooth and thus, we believe it is more consistentin the identification of the components. The recognition ofthe crests depending on the co-expression of other crestsand the relative position of one respect to another (Baileyet al., 2011) would be indeed more problematic in the caseof displaced cusps or atypical shapes. Based on observa-tions of the study sample it is not possible at the OES toreliably differentiate a mesial (i.e., one in which a part ofthe crest meets the marginal ridge) from a middle trigo-nid crest. Therefore, at the OES we only score a middletrigonid crest and a distal trigonid crest, following tradi-tional scoring systems (Korenhof, 1982; Scott and Turner,1997). Furthermore, in those cases where an accessory cusp7 (or metaconulid) is present and spatially belongs to thetrigonid, we consider it as part of the distal segment of themetaconid. Summarizing, and taking into account all theanatomical considerations above, at the OES we recognizefour basic types of trigonid crest expression (Fig. 3):

• type A: a continuous MdTC and an absent or discontinu-ous DTC;

• type B: continuous DTC and absent or discontinuousMdTC;

• type C: continuous MdTC and DTC;• type D: absent or discontinuous MdTC and DTC.

Although both antimeres were analyzed, we employedthe unilateral count method (Turner, 1987), and in caseof asymmetry we have chosen the tooth with the high-est degree of expression for the trait because we considerthat it has more strongly expressed the genetic signal. Sincethe analyzed dental features are minimally affected by sex-ual dimorphism (Turner et al., 1991) both sexes have been

pooled together. We report the inventory of the trigo-nid crest patterns of variation found at the EDJ in the SHmolar sample, as well as the frequencies and percentagesof the trigonid crests pattern at both the OES and EDJ

1/16) 12.5% (1/8) 50.0% (5/10)0.0% 0.0%

anderthalensis; H. sapiens: Homo sapiens.

per molar class. To test for significant correspondence ofthe TC patterns between the OES and the EDJ among SH,H. neanderthalensis and H. sapiens, a non-parametric Chi-square (PAST, Hammer et al., 2001) test is used. For thestatistical analysis of the OES, the data were dichotomizedinto “presence” and “absence” (we considered that the traitis “present” when the crest is continuous, otherwise weconsider that the trait is absent). For the statistical compari-son of the EDJ, we compare the frequencies of “continuous”,“discontinuous”, and “absence”. Results were consideredstatistically significant with a P-value < 0.05.

4. Results

4.1. Trigonid crest types at the OES

Table 2 presents the frequency of expression of a con-tinuous MdTC and DTC at the OES. We observe that thetotality of the SH and Neanderthal M1 and M2 samplespresent a continuous MdTC. For the M3s, this type of crestis present in the 83.3% of the SH sample and the 90% ofthe H. neanderthalensis. Concerning to H. sapiens, almosthalf of the sample analyzed presents this expression ofa MdTC, with the highest value for M1s (50%) and M3s(50%), followed by M2s (25%). Regarding a continuous DTCat the OES, we observe that for the SH sample, these areonly present in the M3s. Meanwhile, the Neanderthal sam-ple is the only one that exhibits continuous DTC in allmolar types, with an increase from M1 to M3. In the sam-ple of H. sapiens, there are no examples with continuousDTC.

The results of analyses of trait frequencies at the OESbetween species are provided in Table 3. If we dichotomizethe expression into present (continuous crest) and absent(discontinuous or absent crest) we observe that SH andNeanderthals possess significantly higher frequencies ofMdTC presence than H. sapiens for the M1, M2 and totalmolar sample. For the M3s, the frequency of a MdTC inH. sapiens is lower but they are not significant. Regarding

the frequency of DTC presence, once again SH and Nean-derthals present higher frequencies for the M3 and for thewhole molar sample. In summary, H. sapiens shows signif-icant differences (P < 0.05) when compared with SH and

M. Martínez de Pinillos et al. / C. R. P

Table 3Chi-square test among SH, Homo neanderthalensis (NEA) and Homo sapiens(SAP) for each tooth position in order to analyze the differences in the traitfrequencies (presence/absence) of MdTC and DTC at the OES.Tableau 3Test du Chi2 parmi les spécimens de SH, Homo neanderthalensis (NEA) etHomo sapiens (SAP) pour chaque type de dent, afin d’analyser les dif-férences entre les fréquences de trait (présence/absence) des MdTC etDTC au niveau de l’OES.

OES (presence/absence)

MdTC DTC

NEA SAP NEA SAP

SHM1 – 0.00a 0.34 –M2 – 0.00a 0.22 –M3 0.62 0.15 0.56 0.02a

Total 0.42 0.00a 0.60 0.00a

NEAM1 0.00a 0.37M2 0.00a 0.20M3 0.09 0.07Total 0.00a 0.01a

Oc

Nq

4

d

TTTT

D

ES: outer enamel surface; SH: Sima de los Huesos; DTC: distal trigonidrest; MdTC: middle and distal trigonid crest.

a Data correspond to P-values (P < 0.05).

eanderthal samples; the former possessing a lower fre-uency of trigonid crest presence than the two latter.

.2. Trigonid crest types at the EDJ

The variety and combinations of trigonid crests on theentine surface of the SH sample is much greater than that

able 4ypology and description of trigonid crest forms identified at the dentine surfaceableau 4ypologie et description des formes de crêtes du trigonide identifiées à la surface

Type 1 Continuous MdTC with an absent or discontinuo

Type 2 Continuous MeTC with an absent or discontinuo

Type 3 Continuous DTC when at least one of the origins

Type 4 Absent or discontinuous DTC when at least oneMeTC or MdTC. The number of distal ridges can

Type 5 Continuous MdTC and a continuous DTC arising

Type 6 Continuous MdTC and a continuous DTC when a

Type 7 Continuous MdTC and a discontinuous DTC whe

Type 8 Continuous MdTC and a discontinuous DTC aris

Type 9 Continuous MeTC and continuous DTC when at

Type 10 Continuous MdTC, a discontinuous DTC when aridge on one side

Type 11 Continuous MeTC or MdTC, a discontinuous DTCdiscontinuous DTC originated from the distal se

Type 12 Continuous MdTC, a discontinuous DTC arising

distal segments

Type 13 Continuous MeTC, a discontinuous DTC arising fdistal segments

Type 14 Continuous MeTC, a discontinuous DTC when atridge on one side

TC: distal trigonid crest; MdTC: middle and distal trigonid crest; MeTC: mesial t

alevol 13 (2014) 205–221 211

expressed at the enamel surface. Table 4 presents compre-hensive typology and description of all types, which arealso illustrated in a schematic form (Fig. 4) and on actualSH specimens (Fig. 5). Table 5 shows that the expressionof the continuous MeTC usually increases from the M1 tothe M3. H. sapiens are the only group with a discontinuousMeTC. For the SH sample we did not record any M1 with acontinuous MeTC. In general terms, the continuous MdTCdecreases its expression from the M1s to the M3s. Overall,M1s from the SH sample present this expression of a MdTC.As it was the case for the MeTC, only H. sapiens exhibits adiscontinuous MdTC. In relation to the continuous DTC onthe dentine, we can observe that this expression is onlypresent in SH and Neanderthals. The H. sapiens sample onlypresents a discontinuous DTC and only in M1s and M2s. Inparticular, all the M2s from SH and 7 of 8 Neanderthal M2spresent a discontinuous DTC.

Table 6 displays the results of analyses of trait expres-sion (continuous/discontinuous/absent) at the EDJ amongspecies. Concerning the MeTC, it is relevant to note thatthere are no significant differences among the three groupswhereas for the MdTC and the DTC, H. sapiens exhibitssignificant differences with the other two. SH sample pos-sesses significantly higher frequencies of MdTC expressionthan H. sapiens for the M1, M2 and total molar sample.Regarding the DTC, SH shows higher frequencies of expres-sion than H. sapiens for the M2, M3 and the total molarsample. Thus, the frequencies of MdTC for the M3s and

DTC for M1s in H. sapiens are lower, but not significant.Meanwhile, Neanderthals shows significantly higher fre-quencies of MdTC and DTC expression than H. sapiens butonly for the total molar sample. For the M1s, M2s and M3s

of the SH sample.

de la dentine de l’échantillon SH.

us DTC

us DTC

is the distal segment, with an absent or discontinuous MeTC or MdTC

of the origins is the distal segment, with an absent or discontinuous be variable

from the middle segments

t least one of the origins is the distal segment

n at least one of the origins is the distal segment

ing from the distal segments

least one of the origins is the distal segment

t least one of the origins is the distal segment, and a pronounced distal

when at least one of the origins is the distal segment, and agments

from the middle segments and discontinuous DTC arising from the

rom the middle segments and discontinuous DTC arising from the

least one of the origins is the distal segment, and a pronounced distal

rigonid crest.

212 M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221

Fig. 4. (Color online.) Scheme of all types of trigonid crests on dentine surface identified in our study from the Sima de los Huesos (SH) molar sample.Explanation in Table 4. View is towards the occlusal surface of the enamel-dentine junction (EDJ) including the tips of the dentine horn (represented bycircles) of the protoconid and metaconid and the mesial marginal ridge (represented by the continuous black line). Dashed lines mean that the crest isabsent or discontinuous.Fig. 4. (Couleur en ligne.) Schéma de tous les types de crêtes du trigonide sur la surface de dentine identifiées dans notre étude sur l’échantillon de molaire

EDJ, inclar une l

SH. Explication dans le Tableau 4. La vue est vers la surface occlusale de l’protoconide et métaconide et de l’arête marginale mésiale (représentée pou discontinue.

the frequencies in H. sapiens once again are lower, but notsignificant.

4.3. Variability of the trigonid crest types at the EDJ

The four basic types of trigonid expression at the OES

contrast with a wider spectrum of crests types and com-binations at the EDJ. As seen in Table 7, type A at the OESis associated with higher variability at the EDJ (10 types),followed by type C (6 types at the EDJ), type D (4 types)

Table 5Frequencies and percentages of the continuous mesial (MeTC), middle (MdTC) anconsider the trait is “present” when the crest is continuous. Otherwise we considTableau 5Pourcentages et fréquences des crêtes du trigonide mésiales (MeTC), intermédiai(un seul antimère inclus).

Total molar sample M1

Mesial trigonid crest at EDJSH 20.9% (9/43) 0.0H. neanderthalensis 20.5% (7/34) 12H. sapiens 7.14% (2/28) 8.3

Middle trigonid crest at EDJSH 72.0% (31/43) 10H. neanderthalensis 76.4% (26/34) 87H. sapiens 39.2% (11/28) 58

Distal trigonid crest at EDJSH 23.2% (10/43) 0.0H. neanderthalensis 14.7% (5/34) 6.2H. sapiens 0.0% 0.0

DTC: distal trigonid crest; MdTC: middle and distal trigonid crest; MeTC: mesial t

uant les pointes de la corne de dentine (représentées par des cercles) designe continue noire). Les lignes tiretées signifient que la crête est absente

and type B (1 type). However, and despite this variability,all teeth generally present a strong correlation between theenamel and dentine surface in the sense that a continuousMdTC at the OES corresponds with a continuous MeTC orMdTC at the EDJ, and vice versa. Similarly, a continuous DTCat the OES tends to correspond with a continuous DTC at

the EDJ.

Type A at the OES (continuous MdTC with absent ordiscontinuous DTC) can be represented at the dentine sur-face by a continuous MeTC or MdTC in combination with a

d distal trigonid crest (DTC) at the EDJ (only one antimere included). Weer that the trait is “absent”.

res (MdTC) et distales (DTC) au niveau de la jonction émail–dentine (EDJ)

M2 M3

% 27.2% (3/11) 33.3% (6/18).5% (2/16) 25.0% (2/8) 30.0% (3/10)% (1/12) 0.0% 25.0% (1/4)

0.0% (14/14) 72.7% (8/11) 50.0% (9/18).5% (14/16) 75.0% (6/8) 60.0% (6/10).3% (7/12) 25.0% (3/12) 25.0% (1/4)

% 0.0% 55.5% (10/18)% (1/16) 12.5% (1/8) 30.0% (3/10)% 0.0% 0.0%

rigonid crest; EDJ: enamel-dentine junction; SH: Sima de los Huesos.

M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221 213

Fig. 5. (Color online.) Examples of different types of trigonid crests on the dentine: type 1 (AT-169); type 2 (AT-1761); type 3 (AT-1945); type 4 (AT-1473);type 5 (AT-2271); type 6 (AT-942); type 7 (AT-141); type 8 (AT-829); type 9 (AT-2438); type 10 (AT-3934); type 11 (AT-2276); type 12 (AT-2270); type 13(AT-557); type 14 (AT-811). Right molar images (type 2, 5, 6, 7, 9 and 11) have been mirrored to facilitate the comparisons.Fig. 5. (Couleur en ligne.) Exemples de différents types de crêtes du trigonide sur la dentine : type 1 (AT-169) ; type 2 (AT-1761) ; type 3 (AT-1945) ; type4 8 (AT-8( roites (l

dMtOoOeia

(AT-1943) ; type 5 (AT-2271) ; type 6 (AT-942) ; type 7 (AT-141) ; typeAT-2270) ; type 13 (AT-557) ; type 14 (AT-811). Les images de molaires da comparaison.

iscontinuous DTC, except in Qafzeh 10 (left M2) where aeTC or MdTC at the EDJ is absent (type 4). Type B (con-

inuous DTC with absent or discontinuous MdTC) at theES corresponds with an absent or discontinuous MeTCr MdTC and a continuous DTC in all cases. Type C at the

ES (continuous MdTC and DTC) corresponds to the co-xpression of two continuous crests also at the EDJ, exceptn AT-100 (left M3) where the MeTC or MdTC at the EDJ isbsent -type 3-, AT-811 (right M3) where the DTC at the EDJ

29) ; type 9 (AT-2438) ; type 10 (AT-3934) ; type 11 (AT-2276) ; type 12des types 2, 5, 6, 7, 9 et 11) ont été réfléchies par un miroir pour faciliter

is discontinuous -type 14- and in Regourdou 1, Krapina D4and Krapina D106 that show at the EDJ a type 2 (MeTC con-tinuous with an absent or discontinuous DTC) crest. TypeD (absent or discontinuous MdTC and DTC) is also relatedon the dentine with an absent or discontinuous MeTC or

MdTC and a discontinuous DTC in all cases except EQ-H5(right M1) where the MdTC is continuous at the EDJ -type11- and MIR4 P22 205 (left M1) where there is a continuousMeTC or type 2 at the EDJ.

214 M. Martínez de Pinillos et al. / C. R. P

Table 6Chi-square test among SH, Homo neanderthalensis (NEA) and Homo sapiens(SAP) for each tooth position in order to analyze the differences in the traitpresence (continuous/discontinuous/absence) of MeTC, MdTC and DTC atthe EDJ.Tableau 6Test du Chi2 parmi les spécimens de SH, Homo neanderthalensis (NEA)et Homo sapiens (SAP) pour chaque type de dent afin d’analyser les dif-férences dans la présence de trait (continu/discontinu/absence) des MeTC,MdTC et DTC au niveau de l’EDJ.

EDJ (continuous/discontinuous/absence)

MeTC MdTC DTC

NEA SAP NEA SAP NEA SAP

SHM1 0.17 0.27 0.17 0.00a 0.38 0.09M2 0.91 0.10 0.91 0.03a 0.22 0.01a

M3 0.85 0.74 0.61 0.08 0.07 0.00a

Total 0.97 0.14 0.66 0.00a 0.08 0.00a

NEAM1 0.72 0.07 0.49M2 0.14 0.05 0.06M3 0.85 0.19 0.12Total 0.19 0.00a 0.02a

DTC: distal trigonid crest; MdTC: middle and distal trigonid crest; MeTC:mesial trigonid crest; EDJ: enamel-dentine junction.

a Data correspond to P-values (P < 0.05).

4.4. Frequencies of expression for the types at the OESand EDJ by tooth class

We have detailed the frequency of the different typesof trigonid crest expression on both enamel and dentinesurfaces for the M1 (Table 8), M2 (Table 9) and M3 (Table 10)samples using the individual count method. In the M1s,the highest frequency of expression at the OES for the SHand Neanderthals samples corresponds to type A, with a100% for the former and all but one specimen for the lat-ter. In contrast, in H. sapiens type A is expressed by half ofthe sample whereas the other half expresses type D. Inter-estingly, type D is absent in SH and H. neanderthalensis. Atthe EDJ, and taking into account that this surface showsmore variability than the enamel, we can observe that themost representative trigonid crest types for the SH, Nean-derthal and H. sapiens samples are type 8, type 10 and type4, respectively.

Concerning the M2s (Table 9) and at OES, we can observethe same pattern for the SH and Neanderthal samples, withtype A being displayed by the totality of the sample in theformer and all but one in the latter. However, for H. sapiens

Table 7Variability of the TC types found at the EDJ and their correspondence tothe OES from all the studied groups.Tableau 7Variabilité des types TC trouvés à la EDJ et leur correspondance au niveaude l’OES de tous les groupes étudiés.

Enamel (OES) Dentine (EDJ)

Type A 1 - 2 - 4 - 7 - 8 - 10 - 11 - 12 - 13 - 14Type B 3Type C 2 - 3 - 5 - 6 - 9 - 14Type D 2 - 4 - 7 - 11

OES: outer enamel surface; EDJ: enamel-dentine junction; TC: trigonidcrest.

alevol 13 (2014) 205–221

the maximum value at the OES is represented by type D(which in turn is absent in SH and Neanderthal M2s) and thelowest by type A (which in turn was the most frequent typein SH and H. neanderthalensis M2s). At the EDJ, the highestfrequencies are for types 11 and 13 for the SH M2s; types7, 10 and 14 for Neanderthals; and type 4 for H. sapiens,which is present by a little more than half of the sample.

With regard to the M3 samples, there is a greater vari-ability between the trigonid crest types on enamel anddentine than in M1s and M2s (Table 10). For the SH sam-ple, the four types are represented, with type C being themost frequent and type D the least. Neanderthals exhibitthe same pattern as the SH sample with the exception thatthey do not display type B. In H. sapiens, half of the samplepresents type A and the other half displays type D. At theEDJ, the highest frequency for the SH M3s corresponds totypes 5 and 6 in Neanderthals corresponds to type 2, andin H. sapiens to type 4.

5. Discussion

5.1. Variability and frequency of expression at the EDJ

Despite a greater variability in the expression of trigo-nid crests at the EDJ (14 types) compared to the OES (4types), in almost all cases there is concordance betweenthe presence of a continuous mid-trigonid and/or distaltrigonid crest at the OES and the presence of a continuousmesial/mid-trigonid and/or distal trigonid crest at the EDJ.As an example, and with only a few exceptions presentedbelow, a type A at the OES (continuous MdTC) always corre-sponds at the EDJ with types where the MeTC or the MdTCis continuous (types 1, 2, 7, 8, 10, 11, 12, 13, 14). Similarly, atype C at the OES (continuous DTC) always corresponds atthe EDJ with types where the DTC – regardless the origin –is continuous. This is particularly useful in the case of wornteeth, because it allows estimation of the type of trigonidcrest pattern that would have been present at the unwornOES.

Regarding the distal trigonid crest at the EDJ, Wu andTurner (1993) did not find individuals expressing both aMdTC and DTC, and Bailey et al. (2011) did not observemolars with a distal-distal configuration (“true” distaltrigonid crest sensu Bailey et al., 2011). Conversely, ourstudy identified several cases of co-expression of MdTC andDTC, and we have also found cases of “true” distal trigonidcrest in SH sample; although they are not very common (2molars or 4.7%) and only M3s display it (Fig. 6). Concern-ing a crest that connects middle and distal segments, Baileyet al. (2011) found only a small number of cases (and only inHomo sapiens) whereas in our analysis we have found fiveM3s from SH sample (11.6%) and four molars from Krapina– one M1, one M2 and two M3s – from H. neanderthalensis(11.8%). However, there are no examples in our H. sapienssample that present this type of trigonid crest pattern.These discrepancies may be related to the limitations oftrying to characterize the variability of a species with small

sample sizes and possibly to some differences in the sco-ring system employed in Bailey et al. (2011) and our study(see Terminological considerations and Scoring proceduressection).

M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221 215

Table 8Frequency of expression of trigonid crests and their percentages on both enamel and dentine for the M1 permanent molars analyzed of Homo heidelbergensis,Homo neanderthalensis and Homo sapiens.Tableau 8Fréquence d’expression des crêtes du trigonide et pourcentages associés sur l’émail et la dentine pour les molaires permanentes M1 analysées issues deHomo heidelbergensis, Homo neanderthalensis et Homo sapiens.

SH Homo neanderthalensis Homo sapiens

OES types n/% EDJ types n/% OES types n/% EDJ types n/% OES types n/% EDJ types n/%

A 14 (100%) 1 1 (7.14%) A 15 (93.75%) 1 0 A 6 (50%) 1 1 (8.33%)B 0 2 0 B 0 2 0 B 0 2 1 (8.33%)C 0 3 0 C 1 (6.25%) 3 0 C 0 3 0D 0 4 0 D 0 4 0 D 6 (50%) 4 4 (33.33%)Total 14 5 0 Total 16 5 0 Total 12 5 0

6 0 6 1 (6.25%) 6 07 2 (14.28%) 7 1 (6.25%) 7 1 (8.33%)8 4 (28.57%) 8 1 (6.25%) 8 2 (16.66%)9 0 9 0 9 010 3 (21.42%) 10 5 (31.25%) 10 1 (8.33%)11 3 (21.42%) 11 3 (18.75%) 11 1 (8.33%)12 1 (7.14%) 12 3 (18.75%) 12 1 (8.33%)13 0 13 0 13 0

14Tot

O s Hueso

mtwcBpowceteHHa

TFHTFi

O

14 0

Total 14

ES: outer enamel surface; EDJ: enamel-dentine junction; SH: Sima de lo

Concerning the origin of the crests that conform theiddle trigonid crest at the EDJ, we can observe that from

he SH molars analyzed (n = 43) there are 31 specimensith MdTC, 20 of which (64.5%) present a middle-middle

rest (see Fig. 7) (i.e., a “true” middle trigonid crest sensuailey et al., 2011) whereas the remaining 11 (35.5%)resent a MdTC of mesial-middle origins. Moreover, inur study we have found that the majority of the molarsith a MdTC show a crest that remains high between the

usps (grade 3 from Bailey et al., 2011), a type that Baileyt al., 2011 found in their Neanderthal sample, but not inheir modern human sample. In accordance with Bailey

t al. (2011), this type of crest was also recorded in our. neanderthalensis sample (67.6%) and it was absent in. sapiens. However, grade 3 (sensu Bailey et al., 2011) waslso present in 77.4% of the SH group.

able 9requency of expression of trigonid crests and their percentages on both enamel anomo neanderthalensis and Homo sapiens.ableau 9réquence d’expression et pourcentages associés des crêtes du trigonide présentssues de H. heidelbergensis, H. neanderthalensis et H. sapiens.

SH Homo neanderthalensis

OES types n/% EDJ types n/% OES types n/% ED

A 11 (100%) 1 2 (18.18%) A 7 (87.5%) 1

B 0 2 0 B 0 2

C 0 3 0 C 1 (12.5%) 3

D 0 4 0 D 0 4

Total 11 5 0 Total 8 5

6 0 6

7 0 7

8 0 8

9 0 9

10 1 (9.09%) 1011 3 (27.27%) 1112 2 (18.18%) 1213 3 (27.27%) 1314 0 14Total 11 To

ES: outer enamel surface; EDJ: enamel-dentine junction; SH: Sima de los Hueso

2 (12.50%) 14 0al 16 Total 12

s.

In addition, among all the molar classes, the M3s arethose with more variability and complexity. Their ratheratypical morphologies (i.e., rotation of the cusps withinthe tooth contour or reduced main cusps in combinationwith accessory cusps) (see Martinón-Torres et al., 2012),prevented in some cases an easy identification of the mor-phological features. As an example, in AT-100 the marginalridge is atrophied and ends at the mesial part of the molar,making it difficult to distinguish whether there is a con-tinuous MeTC or not (Fig. 8). Indeed, most of the casesshowing a “mismatch” between surfaces corresponded toatypical teeth. Despite of this inconvenience, there is a

general concordance in the expression of continuous crestsat the OES and the EDJ, with only some exceptions in whichwhat seems to be a continuous MdTC on the enamel sur-face actually is a discontinuous MeTC at the EDJ (two for

d dentine for the M2 permanent molars analyzed of Homo heidelbergensis,

es sur l’émail et la dentine pour les molaires permanentes M2 analysées

Homo sapiens

J types n/% OES types n/% EDJ types n/%

0 A 3 (25%) 1 00 B 0 2 00 C 0 3 00 D 9 (75%) 4 9 (75%)0 Total 12 5 01 (12.50%) 6 02 (25%) 7 01 (12.50%) 8 2 (16.66%)0 9 0

2 (25%) 10 1 (8.33%) 0 11 0 0 12 0 0 13 0 2 (25%) 14 0tal 8 Total 12

s.

216 M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221

Table 10Frequency of expression of trigonid crests and their percentages on both enamel and dentine for the M3 permanent molars analyzed of Homo heidelbergensis,Homo neanderthalensis and Homo sapiens.Tableau 10Fréquence d’expression et pourcentages associés des crêtes du trigonide présentes sur l’émail et la dentine pour les molaires permanentes M3 analyséesissues de Homo heidelbergensis, Homo neanderthalensis et Homo sapiens.

SH Homo neanderthalensis Homo sapiens

OES types n/% EDJ types n/% OES types n/% EDJ types n/% OES types n/% EDJ types n/%

A 6 (33.33%) 1 0 A 4 (40%) 1 0 A 2 (50%) 1 1 (25%)B 2 (11.11%) 2 1 (5.55%) B 0 2 3 (30%) B 0 2 1 (25%)C 9 (50%) 3 2 (11.11%) C 5 (50%) 3 0 C 0 3 0D 1 (5.56%) 4 1 (5.55%) D 1 (10%) 4 1 (10%) D 2 (50%) 4 2 (50%)Total 18 5 3 (16.66%) Total 10 5 1 (10%) Total 4 5 0

6 3 (16.66%) 6 2 (20%) 6 07 0 7 0 7 08 1 (5.55%) 8 1 (10%) 8 09 2 (11.11%) 9 0 9 010 1 (5.55%) 10 1 (10%) 10 011 1 (5.55%) 11 1 (10%) 11 012 0 12 0 12 013 2 (11.11%) 13 0 13 0

s Hueso

14 1 (5.55%)

Total 18

OES: outer enamel surface; EDJ: enamel-dentine junction; SH: Sima de lo

SH, three for Neanderthals and one for H. sapiens sample)(Fig. 9); and with three H. sapiens molars in which whatseems to be a discontinuous MdTC on the enamel surfaceactually is a continuous MdTC at the EDJ (Fig. 10). As statedabove, it is uncommon and when it occurs it is usually inatypical teeth and often complicated with the expressionof a C7.

5.2. Taxonomical implications

In our study, we have followed some traditional criteria

from the ASUDAS (Turner et al., 1991; Wu and Turner,1993) to score the trigonid crest at the OES (for moredetails see Terminological Considerations above), but wehave also recorded the full variability expressed at the EDJ

Fig. 6. (Color online.) Illustration of a “true” distal trigonid crest at enamel-dentin(AT-2385). Virtual reconstruction of dentine and enamel computer models on miFig. 6. (Couleur en ligne.) Illustration d’une « vraie » crête du trigonide distale auReconstitution virtuelle de modèles de dentine et d’émail informatisés sur un reg

14 0 14 0Total 10 Total 4

s.

to have a more precise knowledge morphological variationin the SH sample. According to Bailey et al. (2002a,b) andMartinón-Torres et al. (2012) the expression at the OES of acontinuous MdTC is a typical Neanderthal feature, but thisfeature is also present in the Middle Pleistocene homininsfossils from Europe like Sima de los Huesos and Arago—butnot in Mauer despite being the holotype of the speciesHomo heidelbergensis. This trait can be also present in ear-lier species like H. erectus, H. georgicus and H. antecessor buttheir expression is less pronounced than in Neanderthalsand the frequencies tend to be lower (e.g., Martinón-Torres

et al., 2007, 2008, 2012; Zanolli, 2013). The pattern ofexpression of this feature at the OES coincides withprevious studies about the OES of SH dentitions that haveshown that these fossils present the classic Neanderthal

e junction (EDJ) and outer enamel surface (OES) in an M3 molar specimencro-computed tomography.

niveau de l’EDJ et de l’OES dans un spécimen de molaire M3 (AT-2385).istre microtomographique.

M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221 217

Fig. 7. (Color online.) Illustration of a “true” middle trigonid crest at enamel-dentine junction (EDJ) and outer enamel surface (OES) in an M2 molar specimen( based oF ermédiaR r un reg

cB2tsowtltcasri

FrFs

AT-946). Virtual reconstruction of dentine and enamel computer modelsig. 7. (Couleur en ligne.) Illustration d’une « vraie » crête du trigonide inteconstitution virtuelle de modèles de dentine et d’émail informatisés su

ombination of traits (Bermúdez de Castro, 1986;ermúdez de Castro et al., 1999; Martinón-Torres et al.,007, 2012). Now, using microCT and virtual segmenta-ions, we can ratify those resemblances at the EDJ. Ourtudy reveals that at the EDJ there is a greater numberf SH molars with a middle or mesial trigonid crest thanithout it, that the middle crest is more frequent than

he mesial one and that there is a high proportion ofower molars with a continuous mesial (MeTC) or middlerigonid crest (MdTC) and a discontinuous distal trigonidrest (DTC), which means a clear predominance of type A

t the OES. This type is also frequent in our Neanderthalample and very rare in our H. sapiens sample, ratifying theesults of Bailey et al. (2011). In addition to the differencesn the frequency of expression, there are six trigonid crest

ig. 8. (Color online.) Enamel and dentine surface of a M3 (AT-100) with an atropeconstruction of dentine and enamel computer models on micro-computed tomig. 8. (Couleur en ligne.) Surface de dentine et d’émail d’une M3 (AT-100) avecpécifique). Reconstitution virtuelle de modèles de dentine et d’émail informatisé

n micro-computed tomography.ire au niveau de l’EDJ et de l’OES d’un spécimen de molaire M2 (AT-946).istre microtomographique.

types that are expressed in the SH and H. neanderthalensisthat are absent in the H. sapiens group (i.e., types 3, 5, 6, 9,13 and 14). If analysis of larger and geographically diversemodern human samples confirms this difference, it maybe of particular utility in the taxonomic assignment ofisolated teeth.

Although a direct comparison between our study andBailey et al. (2011) analysis is not possible because ofthe different scoring systems employed, it was possible tomake some general assessments between both (Table 11).Thus, if we focus on the percentages that show a con-

tinuous MdTC - grade 2 and 3 of Bailey et al. (2011)with a discontinuous DTC, we can assert that the almostconstant expression of this pattern in our SH and Nean-derthals molars in contrast with the low percentages in

hied mesial marginal ridge (MMR) (see text for specific mention). Virtualography.

une arête marginale mésiale (MMR) atrophiée (voir texte pour mentions sur un registre microtomographique.

218 M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221

Fig. 9. (Color online.) Enamel and dentine surface of a M3 (AT-811) with lack of correspondence (see text for specific mention). Virtual reconstruction of

(AT-81tine à pa

dentine and enamel computer models on micro-computed tomography.Fig. 9. (Couleur en ligne.) Surface de l’émail et de la dentine d’une M3

Reconstruction virtuelle de modèles informatiques pour l’émail et la den

our H. sapiens sample, is in concordance with the resultspresented by Bailey et al. (2011) (Fig. 11). Indeed, when acontinuous MdTC is present in other group rather than SHor H. neanderthalensis, the crests are low and dip further atthe sagittal sulcus (this study; Bailey et al., 2011; Zanolliand Mazurier, 2013). As previously stated by Bailey et al.,2011, the structures underlining the MdTC in the dentinetend to be different to the ones that contribute to the mid-dle trigonid crest in other hominin species (Bailey et al.,2011). As an example, the expression of a continuous MdTC

at the EDJ in other groups such as Pan, A. africanus, Homosapiens (Bailey et al., 2011) or the North African MiddlePleistocene hominins from Tighenif (Zanolli and Mazurier,2013) is usually associated to a grade 2. In addition, the

Fig. 10. (Color online.) Enamel and dentine surface of a M1 (EQ-H5) with lack of

dentine and enamel computer models on micro-computed tomography.Fig. 10. (Couleur en ligne.) Surface de l’émail et de la dentine d’une M1 (EQ-HReconstruction virtuelle de modèles informatiques pour l’émail et la dentine à pa

1) avec absence de correspondance (voir le texte pour plus de détails).rtir de données microtomographiques.

expression of a continuous MdTC in H. sapiens is never asso-ciated with a grade 3 (this study; Bailey et al., 2011).

We have also identified a wide spectrum of trigonidcrest types at the EDJ. Importantly, there are three trigo-nid crests types (types 3, 9 and 13) that are only presentin the SH sample and have not been found in the Nean-derthal or the H. sapiens group. Future studies in largersamples are necessary to know whether these SH exclu-sive types are present in other hominin groups or if theyare particular to the SH group. If they are present in earlier

hominins it would mean SH retains some primitive fea-tures that are lost in classic Late Pleistocene Neanderthals,as it happens with other cranial and postcranial elements(Arsuaga et al., 1997). On the contrary, if it is confirmed

correspondence (see text for specific mention). Virtual reconstruction of

5) avec absence de correspondance (voir le texte pour plus de détails).rtir de données microtomographiques.

M. Martínez de Pinillos et al. / C. R. Palevol 13 (2014) 205–221 219

Table 11Comparison between the data of our samples and those from Bailey et al. (2011) regarding continuous or discontinuous MdTC.Tableau 11Comparaison entre les données issues de nos échantillons et celles présentées dans Bailey et al. (2011) en ce qui concerne les MdTC continues ou discontinues.

This study Bailey’s data

SH sample H. neanderthalensis H. sapiens H. neanderthalensis H. sapiensn % n % n % n % n %

Enamel (OES)MdTC continuous (grade 2-3, Bailey et al., 2011) 40 93.02 33 97.05 11 39.28 61 100 8 11.76MdTC discontinuous (grade 1, Bailey et al., 2011) 3 6.97 1 2.94 3 10.71 – – 13 19.11

Dentine (EDJ)MdTC continuous (grade 2-3, Bailey et al., 2011) 40 93.02 33 97.05 13 46.42 72 98.63 24 35.29MdTC discontinuous (grade 1, Bailey et al., 2011) 3 6.97 1 2.94 6 21.42 1 1.36 8 11.76

OES: outer enamel surface; EDJ: enamel-dentine junction; SH: Sima de los Huesos; MdTC: middle and distal trigonid crest.

Fig. 11. Illustrations of differences among specimens for grades of presence of middle trigonid crest (MdTC) at the outer enamel and enamel-dentinejF de présed

tgattPT

6

Ettdhcg

unction surfaces.ig. 11. Illustration des différences entre les spécimens selon les degrés

e la EDJ.

hat those types are not present in any other homininroup, they should be considered as derived (and maybeutopomorphic) features for the SH hominin group, andhey would ratify the highly derived state of this popula-ion with regard to H. neanderthalensis (Gómez-Robles andolly, 2012; Gómez-Robles et al., 2007, 2008; Martinón-orres et al., 2012).

. Conclusions

In agreement with Bailey et al. (2011) and because theDJ exhibits a greater number of trigonid crest types thanhe enamel, we developed a comprehensive scoring sys-em to characterize trigonid crest patterning in the Sima

e los Huesos lower molar sample. Our analysis revealsigher variability of trigonid crest expression at the EDJompared to the OES; however, our results confirm theeneral concordance between the two surfaces with regard

nce des crêtes du trigonide intermédiaires (MdTC) au niveau de l’OES et

to the expression of continuous mesial/middle and distaltrigonid crests (Bailey et al., 2011; Skinner et al., 2008b).Thus, the manifestation of the trigonid crest patterns atthe enamel is mostly determined by the development ofthe EDJ. This fact is particularly relevant as it allows pre-diction of the type of trigonid crest pattern at the OES inthe case of excessively worn teeth. This also maximizes thenumber of teeth that can be analyzed, enlarging the sam-ple size particularly in the case of the scarce fossil humanremains.

In concordance with previous studies based on the OESmorphology, our study confirms that SH displays trigonidcrest patterns that have been classically considered as typ-ical of H. neanderthalensis and significantly different from

H. sapiens. However, it has also shown some trigonid cresttypes that were present neither in the H. neanderthalensissample nor in the H. sapiens sample. Analysis of otherPleistocene hominins will improve the taxonomic and

l. / C. R. P

220 M. Martínez de Pinillos et a

phylogenetic information about these traits, as well as, tomake possible evolutionary inferences about the expres-sion of these traits in relation with other ancestralhominins.

Acknowledgments

We thank all the members of the Atapuerca researchteam, in particular those who excavate the Sima de losHuesos site, for their laborious and dedicated work. Wealso acknowledge several people for providing access tothe studied material and for their helpful assistance:R. Macchiarelli, P. Bayle and P. Semal from NESPOS society;E. Carbonell and M. Lozano (Institut Català de Paleoecolo-gia Humana i Evolució Social, Tarragona, Spain). We arealso grateful to G.R. Scott for valuable revisions and instruc-tive comments that have definitely helped to improve themanuscript. We also recognize the inestimable help ofP. Fernandez and E. Lacasa from the Restoration and Con-servation Laboratory of the CENIEH, and M.C. Ortega fromCentro de Evolución y Comportamiento Humanos (ISCIII,Madrid) for the restoration and conservation of the SHcollection. We are also grateful to M. Modesto from theCENIEH for his suggestions in the statistical analysis. ThemCT scanner of the SH, Mirador and CENIEH dental collec-tion were performed at CENIEH with the collaboration ofCENIEH staff. We want to recognize the inestimable helpof two anonymous reviewers and the editor for their con-structive comments. Any error is solely the responsibilityof the authors.

This research was supported with funding from theDirección General de Investigación of the Spanish Mini-sterio de Educación y Ciencia (Project N CGL2009-12703-C03-01); Secretaría de Estado, Investigación, Desarrolloe Innovación of the Spanish Ministerio de Economía yCompetitividad (Project N CGL2012-38434-C03-02); Con-sejería de Educación de la Junta de Castilla y León (ProjectCEN074A12-1) and the Leakey Foundation. Fieldwork atAtapuerca is supported by the Consejería de Cultura y Tur-ismo of the Junta de Castilla y León and the FundaciónAtapuerca. We are also grateful to the altruistic help ofFundación Caja Rural de Burgos in the investigation issues.M.M-P. has the benefit of a predoctoral grant of the Fun-dación Atapuerca.

Grant sponsorship: Spanish Ministry of Ciencia e Inno-vación, Ministry of Culture of the Junta de Castilla y León(Spain), Fundación Atapuerca, Leakey Foundation.

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